The present invention relates to the art of electric arc welding and more particularly to an electric arc welder having an arc starter and the method of utilizing the arc starter for initiating the welding operation.
The invention involves an addition to an electric arc welder, such as a MIG welder, to start the welding arc with virtually no spatter. Arc starting techniques are quite common in TIG welding where a non-consumable electrode is employed for creating an arc to melt filler used in the welding process. Starting of a TIG welder is explained in the introductory portion of Heraly U.S. Pat. No. 6,034,350, which is incorporated by reference herein as background technology regarding arc starting, even though the Heraly patent discusses only TIG welding. In this background technology, numerous approaches are explained to start a TIG welding arc. The most popular technique is a high frequency voltage to initiate and maintain the arc between the electrode and workpiece. The high frequency voltage ionizes the gas, thus allowing the welding power to jump the gap between the electrode and workpiece. As explained in this well known background technology, such high frequency starting arrangements have drawbacks. To overcome these drawbacks, TIG welding has used scratch starting where the non-consumable electrode is scratched over the workpiece to create an arc. To overcome the problems associated with such starting, the ground technology discusses a lift arc starting method where a separate low current power circuit creates a small monitored voltage between the electrode and workpiece. When the non-consumable electrode is in engagement with the workpiece, the voltage from the low current power supply warms the electrode. When the electrode is withdrawn, the main power circuit is immediately initiated to provide power between the tungsten electrode and workpiece. However, as described in the background technology, such lift arc starting methods fail to reliably regulate the welding operation. Consequently, Heraly U.S. Pat. No. 6,034,350 is incorporated by reference herein only for its showing of background information associated with TIG welding and starting of the arc for such welding. TIG welding, when using lift starting of the arc, monitors only the voltage and controls the main power supply based upon the voltage. This background technology for the welding assists in understanding the present invention but does not teach the novel concept of this invention allowing it to be especially beneficial for welding with a consumable electrode.
Stava U.S. Pat. No. 5,148,001 discloses an electric arc welder used for STT welding as popularized by The Lincoln Electric Company of Cleveland, Ohio. In this patent there is disclosed a low current high inductance circuit in parallel with the primary power source. The inductance of the secondary circuit is quite high compared to the inductance of the choke in the main welding circuit. In this prior patent, the inductance of the secondary circuit is 0.5 henry compared to the choke having an inductance of 7.0 microhenries. This Stava patent discloses a secondary, high inductance current for maintaining the arc-during STT welding. This patent is incorporated by reference herein for this general technology used in a welding process involving a consumable electrode and short circuit transfer. Stava does not suggest the novel concept of the present invention which does incorporate a separate high inductance power supply, but the parallel current path is used differently.
In electric arc welding, such as MIG, Stick and submerged arc welding, it is desirable to start the arc between the consumable electrode and the workpiece in a manner to reduce spatter. Starting concepts for TIG welding are quite well known as described in the patents incorporated by reference herein; however, these starting concepts are not generally applicable to consumable electrode welding. Such consumable electrode welding still needs to have an efficient start of the arc at the inception of the welding process; however, the TIG welding concepts are generally not applicable and add complexity to the welding equipment. However, the use of a low current high inductance background circuit in parallel with the primary source of current, as suggested in STT welding, presents an advantage when welding with consumable electrodes. Since the loss of a welding arc during the welding process is primarily due to a lack of voltage, such secondary high inductance background current maintains the arc when the voltage from the main power supply is not high enough to maintain the total arc plasma voltage. The total plasma voltage includes the anode and cathode voltage, plus the voltage gradient in the arc itself. In the past, the arc would be extinguished when its arc length exceeded the available voltage from the main power supply. The use of a secondary power supply, such as shown in Stava U.S. Pat. No. 5148,001, allows the welding to maintain the arc even during instantaneous increases in the arc length greater than can be handled by the main power supply. Consequently, when using a parallel high inductance power supply as shown in Stava U.S. Pat. No. 5,148,001, the dynamics of the welding process that often create long arc lengths momentarily need not have a power supply that is large enough to meet the arc requirements during periods of such arc length increases. In other words, the use of a background or parallel source of high inductance power is quite beneficial in welding operations having consumable electrodes. However, heretofore, such parallel high inductance supply of power has not been used for arc starting.
The benefit of using a parallel high inductance power supply for electric arc welding in a consumable type of welding operation is realized because such power supplies generally use a choke in the output circuit. One purpose for this choke is to provide the voltage needed to maintain the arc, as previously described. However, another purpose of the choke is to prevent the output current from changing too rapidly for protecting circuit components from excessive current due to instantaneous load changes. The choke helps stabilize the arc as well as maintain the arc. Consequently, the use of the choke in the welders requires that the choke has a high enough inductance to supply the voltage for long arc lengths to maintain the arc, yet small enough to allow the current to change quickly when required by the welding process. These two requirements of the choke are divergent and conflict with each other. For this reason, the use of a parallel circuit, as shown in Stava U.S. Pat. No. 5,148,001, wherein a second high inductance circuit provides the voltage to maintain the arc at long arc lengths, does not interfere with the ability of the main power supply to quickly alter its current. Of course, if the power supply trends to a low the current below the set current of the high inductance background or secondary power supply, the background current takes over to give a minimum current. All of these advantages obtained by the use of a secondary power supply when used in consumable electrode welding does not relate to improved arc starting which is the subject of the novel aspects of the present invention.
The present invention relates to the use of a secondary power supply, as generally taught by Stava U.S. Pat. No. 5,148,001, with additional technology and components to facilitate starting without spatter. The secondary power supply is started with the main power supply off and after the consumable electrode touches the workpiece. This causes low current flow between the consumable electrode and the workpiece. With this low current flow, the electrode is pulled away from the workpiece to create a small arc, especially in the presence of shielding gas. The secondary or background power supply maintains current flow between the electrode and workpiece to cause the electrode and workpiece to be heated. This heating operation is not sufficient to melt the electrode, but does establish a heated vapor between the workpiece and electrode. To assure that enough heat has been applied before the main supply is enabled, the present invention involves the calculation of Joules created between the electrode and workpiece. The total Joules or total heat created at the electrode and workpiece is compared to a set value. Consequently, when the calculated Joules or total heat equals or exceeds a set point, a signal is generated to enable the main power supply. At the same time the wire feeder is started. The welding then proceeds in accordance with standard practice.
An advantage of this method is that the calculated total heat which is compared to a set point heat will compensate for different arc lengths and different shielding gas. In view of the integration feature, voltage spikes are ignored to give a noise free signal. Also, this process is used for arc initiation in semi-automatic or manually welding; however, it is also applicable to robotic automatic welding. The novel arc starting equipment and method is used with an electrode that is steel, stainless steel, steel alloys, aluminum, aluminum alloys, nickel alloys, silicon bronze and other metals. The new arc starting equipment and method is applicable to tubular electrodes, as well as solid wire electrodes. This starting system and method can be used with any welding process using a consumable electrode. However, it is also applicable to non-consumable electrode welding processes, such as TIG welding.
In accordance with an aspect of the invention, the electrode wire feeder is started when the main power supply is started. Consequently, in MIG welding, the novel starter and method of starting the arc turns on the main power supply and also initiates the wire feeder. The novel electric arc welder comprises a main power supply having an off condition directing no current across an electrode and workpiece and an on condition directing welding current between the electrode and workpiece through a choke and a secondary power supply with a switch closable to apply a given current through a series circuit including a high inductance inductor, the electrode and the workpiece. The welder is provided with a sensor to sense the instantaneous current from the secondary power supply and a sensor to sense voltage between the electrode and workpiece. A multiplier circuit has a first input for the instantaneous current and a second input for the voltage and an output constituting the product of the instantaneous current and voltage. This provides a signal having a value representing the watts being created by the secondary power supply. A circuit integrates the watt signal to provide a time function output signal representing the accumulated heat between the electrode and workpiece. A comparator circuit with a first input for the time function signal and a second input for a fixed value reference signal produces an output switching signal when the time function signal equals and/or exceeds the reference signal so the main power supply can be shifted to the on condition when the power supply receives the switching signal from the comparator. To operate the welder, the electrode is touched against the workpiece and the secondary power supply is turned on by closing the switch. Thereafter, the total heat at the electrode and workpiece is accumulated. After a short period of time of less than five seconds, the electrode is pulled away from the workpiece while the total heat is being accumulated. When the total heat reaches a set reference value, the main power supply is turned on. At the same time, when a wire feeder is used for the electrode, the wire feeder is also activated. This provides an arc starting procedure based upon total heat between the electrode and workpiece, as opposed to time and/or voltage as used in prior art.
In accordance with another aspect of the present invention there is provided a method of starting an electric arc welder comprising an electrode movable between a first position touching a workpiece for a given time and a second position pulled away from the workpiece after the given time. The electric arc welder has a main power supply having an off condition directing no current across the electrode and workpiece and an on condition directing welding current between the electrode and workpiece through a choke. A secondary power supply has a switch that is closable to cause the secondary power supply to apply a given current through a series circuit including a high inductance inductor, the electrode and the workpiece. This type secondary background current power supply is similar to the secondary power supply shown in Stava U.S. Pat. No. 5,148,001; however, in the present invention it is preferred that the secondary power supply be powered by a different input source than the main power supply. In addition, the secondary power supply has a switch which allows operation of the secondary power supply separately from the main power supply. This feature is used by the present invention and is not disclosed or suggested by the Stava patent.
In accordance with an aspect of the invention, the wire feeder of the electrode is operated at the same time as the main power supply is activated. In accordance with the invention the given time for the electrode to touch the workpiece is in the general range of less than 5.0 seconds. The low current of the secondary power supply is in the general range of 2-5 amperes. Of course, the inductance of the choke is drastically less than the inductance of the inductor in the secondary power supply circuit. The general ratio of such choke and inductor is the inductance values disclosed in Stava U.S. Pat. No. 5,148,001.
The primary object of the present invention is the provision of a welder with an arc starter, which arc starter can be used for consumable electrodes to provide reduced spatter.
Another object of the present invention is the provision of a welder, as defined above, which welder includes a secondary power supply having a low current, high inductance that prevents arc extinguishing during long arc lengths and also allows arc starting after a predetermined total heat.
Still a further object of the present invention is the provision of an electric arc welder, as defined above, which electric arc welder can be used by a variety of consumable electrode welder with a variety of different consumable electrodes.
Yet another object of the present invention is the provision of an electric arc welder, as defined above, which electric arc welder can also be used for starting an arc in a TIG welder by measuring the total temperature between the electrode and workpiece and applying the main power supply when the total heat reaches a certain value.
Another object of the present invention is the provision of a method of starting an electric arc in an electric arc welder which does not involve merely turning the welder on, but also involves measuring the total heat prior to the welder being turned on.